Twilight of America's grasslands.
Henslow's sparrow, in birdwatcher lingo, is an LBJ or little brown job: one of those cryptically colored songbirds that are annoyingly adept at revealing themselves for only a split second, defying identification. At times it behaves more like a mouse than a bird, scurrying through the grass. Field-guide maven Roger Tory Peterson once remarked, "Were it not for its song, this bird would go almost undetected."
Song? Only in a literal sense. Henslow's sparrow shyly announces itself with an insectlike hiccup (se-LICK) that would mortify most other sparrows--a clan that includes a couple of nature's finer musicians. But to defend its territory, the secretive bird "will get atop a dead plant from last summer and sing its guts out," says Lori Pruitt, a U.S. Fish and Wildlife Service biologist in Bloomington, Indiana, whose mission last year was to assess Henslow's sparrow as a possible candidate for the federal Endangered Species List.
While the bird is still common enough to make listing unlikely anytime soon, no one doubts that the species, whose continent-wide breeding population is estimated to have declined by 93 percent during the past 30 years, is in serious trouble. Indeed, Henslow's sparrow serves to dramatize the plight of many of the songbirds that nest in North American grassland habitats, from the shortgrass prairie that rubs against the Rocky Mountains to the few hayfields that still sit atop New England's weathered hills.
"Grassland birds exhibit the most consistent, widespread and steepest declines of any habitat group," says Bruce Peterjohn, coordinator of the North American Breeding Bird Survey (BBS). He points out that only 10 percent of all grassland species show positive population trends. In contrast, more than 50 percent of bird species that nest in forests have increased in numbers since 1966, the year of the first BBS counts. "These declines are prevalent from the Great Plains eastward across the United States and southern Canada," Peterjohn emphasizes, "and they probably began long before the BBS was conceived."
A part of the Biological Resources Division of the U.S. Geological Survey, the BBS depends on 2,000 expert volunteers who, at the peak of every nesting season, count birds along permanent routes in order to track population changes. BBS projections for a few grassland species in addition to Henslow's sparrow underscore what Van Remsen, an ornithologist at Louisiana State University, calls "America's most neglected conservation problem."
The bobolink, whose aerial courtship song bubbles like aural champagne over hayfields and old pastures--down 37 percent across its range since 1966.
The eastern meadowlark, the original fence-sitter, with its natty sunflower vest and black cravat--down 53 percent.
The grasshopper sparrow, whose buzzy vocalizations are above the hearing range of some birdwatchers--down 66 percent.
Sprague's pipit, which spends the spring months aloft, broadcasting the sound of tinkling sleighbells across northern prairies--down 75 percent.
The disappearance of once-familiar species often is more acute at the state level. Illinois, for example, has lost 94 percent of its nesting bobolinks. Grasshopper sparrow numbers have plummeted by 96 percent in New York. Moreover, many North American grassland birds are short-distance migrants. They winter mainly in the Sunbelt states, which means their population declines are not due to problems in Latin America, as is the case in part with some forest birds. We can't blame anyone but ourselves, prairie-bird experts say.
And there's no mystery at all about the underlying cause: Land development, primarily for agriculture, has destroyed or degraded vast stretches of the birds' grassland habitat leaving the animals bereft of home and food. Consider Henslow's sparrow, whose story could be adapted for other troubled grassland species with only a few small changes. Once a fairly common summer resident across the northern tier of states from southern Minnesota, Iowa and eastern Kansas to the Atlantic Seaboard, Henslow's sparrow essentially has disappeared from the Northeast. It now appears on the threatened-species list in Illinois, where it was one of the most abundant prairie birds a century ago.
Henslow's sparrow nests in loose colonies in meadows and fields with several necessary features: tall, dense grass; sturdy, dried-up forbs from the previous summer that can be used as singing perches; and a deep litter layer where the bird can forage for seeds and insects like crickets, hide its nest and escape from predators. Before pioneer sodbusters arrived, tallgrass prairie was the species' primary habitat. Illinois, for example, had 21 million acres of native prairie prior to Euroamerican settlement, but now only a few tracts survive, totaling about 2,500 acres.
However, as biologist Jim Herkert of the Illinois Endangered Species Board points out, "Prairie birds are resilient." Henslow's sparrow and its neighbors like the eastern meadowlark and bobolink adapted to breeding in hayfields and pastures, expanding their range all the way to New England wherever forests had been cleared for farms.
Now, those agricultural grasslands also are disappearing--lost to development, planted in more profitable row crops or reverting to forest as farms are idled. In Illinois, millions of acres of oats, hay and pasture have been converted to soybean production since the 1960s. Worse, the new alfalfa varieties that farmers are planting permit earlier and more frequent mowing, turning hayfields into death traps for nesting birds. "Hay-cutting begins before the birds have a chance to raise their broods, and there's not enough time between mowings for a second nesting attempt to succeed," says Herkert. In a New York study, hay-cropping caused the loss of 94 percent of bobolink nests, while in undisturbed fields, 80 percent of boblink nestlings survived.
The bad news continues. Pruitt reports, "The highly fragmented nature of remaining grassland habitats has serious implications for area-sensitive species." A study by Peter Vickery, a Massachusetts Audubon Society ecologist, concludes that a site must be a minimum of 500 acres "to support a diverse grassland bird fauna." Herkert searched 24 areas in Illinois and found Henslow's sparrows breeding on just one grassland patch smaller than 250 acres.
But the knockout blow for Henslow's sparrow could be the loss of the species' wintering places on the coastal plain from East Texas to Florida: open pine woods with a thick grassy undercover and stretches of savannahs and prairies. Pruitt reports that 97 percent of the natural longleaf pine forest in the Southeast, once the region's dominant ecosystem, has been converted to industrial tree plantations or row crops. Similarly, more than 99 percent of the tallgrass prairie in Louisiana and Texas has been destroyed.
No one has ventured an estimate of the total Henslow's sparrow breeding population, but Pruitt says only four areas in the country are home to colonies totaling 400 or more nesting pairs: a complex of prairie preserves in southwestern Missouri; The Nature Conservancy's Tallgrass Prairie Preserve in Oklahoma; Fort Riley, an Army base in Kansas; and Jefferson Proving Ground, a closed military facility in southern Indiana.
Henslow's sparrow thrives at Jefferson only because large areas of the base were burned periodically to reduce the risk of wildfire from ordnance testing. In fact, scientists stress that grasslands and their bird communities need cyclic disturbance by prescribed burns, grazing or mowing. Further, grassland conservation areas require intensive management to create the mosaic of microhabitats favored by different bird species.
"We have three study plots on The Nature Conservancy's tallgrass preserve that haven't been burned or grazed for seven years, and those grasslands are now very dense," says Don Wolfe, a biologist at the Sutton Avian Research Center in Bartlesville, Oklahoma. "A lot of the birds we found early on are no longer present." The grasshopper sparrow, for instance, prefers to nest in recently burned areas and moves out in three or four years, about the time the vegetation becomes suitable for Henslow's sparrow. And dickcissels seek the woody growth offered by mature grasslands.
Researchers at the Colorado Bird Observatory near Denver, meanwhile, have demonstrated that shortgrass prairie birds also require a mix of habitats: mountain plovers nest on bare ground; horned larks and McCown's longspurs are associated with sparse grass in heavily grazed areas; vesper sparrows like dense grass but height does not matter; western meadowlarks prefer both tall forbs and tall dense grass; and Cassin's sparrows and lark buntings are found in shrubby areas.
"Grazing is essential for maintaining shortgrass prairie," says Jim Bradley, who studied bird populations on the Comanche and Pawnee National Grasslands in Colorado and at the Thunder Basin National Grassland in Wyoming. "The question is, what kind of grazing? Instead of free-roaming herds of bison and pronghorns that left large areas of prairie ungrazed for a few years, we have herds of cattle confined behind wire fencing. The Pawnee grassland, for example, has become very homogeneous habitat." Bradley says he and his colleagues hope to work with the U.S. Forest Service, which manages the national grasslands, to provide adequate habitat for bird species on the eastern plains of Colorado and Wyoming.
Macro-management for grassland birds already is the plan at the Forest Service's new Midewin National Tallgrass Prairie on the site of the former Joliet Army Ammunition Plant near Chicago. During World War II, the Illinois arsenal produced 5.5 million tons of TNT weekly, and it was reactivated during the Korean and Vietnam wars. Now, 5,000 acres that never saw a plow but were planted in fire-resistant bromegrass for leased pasture will be restored as the largest contiguous block of native tallgrass prairie in the upper Midwest. "We'll reintroduce fire, allow the native grasses and wildflowers to return, and put back the elk and bison that were here when the settlers arrived," says ecologist Larry Stritch. "Midewin is so huge that we can design large blocks of habitat that will appeal to birds whose needs have a unique little twist."
Midewin Prairie (pronounced "mid-A-win" and named after a Potawatomi Indian healing society) isn't the only upbeat news on the grassland bird front. The U.S. Fish and Wildlife Service is planning a new kind of national wildlife refuge--a Northern Tallgrass Prairie Habitat Preservation Area that, through land purchases and easements, will encompass some 70,000 acres of scattered prairie remnants in Iowa and Minnesota.
But those kinds of opportunities are rare. "It's not possible to buy and restore enough native prairie to reverse the decline of grassland birds," says Sam Droege, a biologist at Patuxent Wildlife Research Center in Laurel, Maryland. "The conservation community has to respond with a new approach that focuses on cooperative efforts with private owners to make agricultural lands more bird-friendly." Droege points to the success of a University of Wisconsin project in which dairy farmers set aside a third of their pasture as a refuge for grassland birds, waiting until after the nesting season to mow or graze the acreage.
Another positive note is last year's renewal by Congress of the Cropland Reserve Program, under the Farm Bill, which has created millions of acres of temporary nesting space and given a boost to populations of some grassland bird species in the row-crop desert of the northern plains.
Friends of the little brown jobs and of their more colorful and charismatic neighbors could use a few more reasons for optimism.
A nearby hilltop meadow full of singing bobolinks, meadowlarks and savannah sparrows is Field Editor Les Line's favorite haunt on blue-sky days in late May.
The current plight of grassland birds, says one expert, is the most neglected conservation problem in America
Species on the Edge
The following 28 native bird species (plus an adopted pheasant) live predominantly in grasslands. Fully
half of these birds show declining population trends continent-wide, based on North American Breeding Bird Survey (BBS) data from 1966 to 1995, while only three species show increasing numbers. In three cases, BBS records are too few to make a trend projection*.
Ferruginous hawk Northern harrier Greater prairie chicken (NA) Sharp-tailed grouse Ring-necked pheasant Mountain plover (NA) Long-billed curlew Upland sandpiper Barn owl (NA) Burrowing owl Short-eared owl Horned lark Sedge wren Sprague's pipit Bobolink (above) Eastern meadowlark (left) Western meadowlark Dickcissel Lark bunting Savannah sparrow Grasshopper sparrow Baird's sparrow LeConte's sparrow Henslow's sparrow Cassin's sparrow Vesper sparrow McGown's longspur Chestnut-collared longspur *Key: Declining Increasing Stable Insufficient data (NA)
For More About Grasslands
Grasslands once covered 40 percent of the United States, but much of that expanse has been lost to the plow. The tallgrass prairies of the central Midwest, in which some species grew 10 feet tall, have been reduced by 99 percent. The National Wildlife Federation is working to focus public attention on the nation's beleaguered grassland ecosystems. This year, the U.S. Forest Service will consider revisions to management of national grasslands under its jurisdiction. If you would like to keep abreast of this and similar actions affecting national grasslands, contact: National Wildlife Federation Rocky Mountain Natural Resources Center, 2260 Baseline Road, Suite 100, Boulder, Colorado 80302.
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|Date:||Apr 1, 1997|
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